This invention deals with the general domain of control processes of an expansion valve placed in an air conditioning circuit or loop in which circulates a sub-critical cooling fluid (R-134a, R-1234yf for instance). In general, such an air conditioning circuit includes at least a fixed or variable capacity compressor, an expansion valve, a condenser and an evaporator. Optionally, such an air conditioning circuit can include an internal heat exchanger between the high pressure and low pressure parts of the air conditioning circuit.
The invention deals more specifically with the strategy for controlling the expansion valve of an air conditioning circuit of an air conditioning system to be implemented in an automotive vehicle.
Control of the expansion valve opening enables to control overheating and under-cooling directly or indirectly so as to optimize the energy efficiency of the air conditioning circuit. Control of the expansion valve opening also permits to protect the air conditioning circuit from temperature and pressure peaks at the compressor outlet.
There are multiple solutions to control the expansion valve opening. According to these solutions, overheating, in other words, the difference in temperature at the evaporator outlet and the fluid saturation temperature, is controlled by using a derived integral proportional command. It is also possible to control the expansion valve opening on the basis of the temperature at the compressor outlet.
These solutions pose a problem for the weak thermal charges (for instance for outside temperatures below 25° C.). Indeed, it is very difficult to obtain overheating or under-cooling when the outside air temperature is below 25° C. Rather, one observes a temperature unbalance when exiting the evaporator and/or an increase in the system instability. In such case, checking the overheating does not make sense since this overheating is near the zero value.
If, on the other hand, a control of under-cooling is looked for at the inlet of the expansion valve, this cooling is also nearly zero during climate conditions showing an outside temperature below 25° C. for instance.
Consequently, the main purpose of this invention is to overcome the inconveniences or problems of the known systems by proposing a control process for an expansion valve situated on an air conditioning circuit in which a cooling fluid circulates, with the air conditioning circuit comprising at least a compressor, a condenser and an evaporator cooling, with this control process comprising the following steps:
when overheating is less than a threshold value, opening of the expansion valve is governed by a static control, and
when the overheating is higher than the threshold value, opening of the expansion valve is governed by a dynamic control.
Consequently, with the invention, a static control of opening the expansion value is performed as soon as the overheating or the sub-cooling is near zero and thus difficult to control.
On the other hand, when the overheating or the sub-cooling is controllable, which corresponds to a difference between the temperature or pressure at the compressor outlet and a predetermined temperature or pressure threshold, higher than a predetermined elementary offset, if the parameter to control is higher than its set point value, the expansion valve is controlled dynamically on the basis of this parameter.
This way, the inconveniences of the systems of the state of the art, in which the absence of overheating or sub-cooling prevents an efficient control of the air conditioning circuit for controlling the opening of the expansion valve.